public class Exam3_3 {
    public static void main(String args[]) {
            double sum = 0;
            for(int i=1;i<=20;i++) {
                    sum = sum+1.0/fact(i);
            }
            System.out.println(sum);
    }
    public static int fact(int n) {
            if(n==0)
                    return 1;
            else
                    return n*fact(n-1);
    }
}
